1. Field of Invention
The invention relates to the structure of a flexible printed circuit for inkjet printheads and the manufacturing process therefor, so that a deflecting process can be properly performed during the cartridge manufacturing process. It can avoid the crook problem due to collision damages and residual stress in subsequent manufacturing processes or uses.
2. Related Art
The inkjet printhead relies upon the connection between a flexible printed circuit and the printer to transmit the control signals, and thus accurately eject ink to print desired texts or pictures. The assembly of the flexible printed circuit requires deflecting the flexible printed circuit at about the right angle to the side of the inkjet chip.
Current flexible printed circuits are either two-layered or three-layered, and polyamide are used mainly as their substrates. Both of them are coated with a layer of copper or copper alloy on the substrate to form a conductive circuit layer. The difference between these two specifications is in the materials, manufacturing process of the copper conductive circuit and the method of attaching copper or copper alloy onto the polyamide. For those with two-layer structures, the substrate surface is treated with sputtering, evaporation, etc to form a metal layer (e.g. Ni, Cu, and their alloys). The metal layer is then etched using a photolithography process to form a conductive circuit. Afterwards, it is electroplated with a metal such as copper. For those with three-layer structures, the soft substrate surface is further laminated with a metal layer such as a copper foil. The photolithography and etching means are then employed to form a conductive circuit. To prevent the conductive circuit from oxidation or scratches, the completed circuit is selectively covered with a hot plating, solder-mask material, photosensitive material, or metal layer. In general, no matter what kind of flexible printed circuit is chosen, certain rigidity defies against deflection.
Therefore, to ensure the smooth attachment between the flexible printed circuit and the ink cartridge during the flexible printed circuit assembly of the inkjet printhead so that the automatic equipment can precisely align the attachment position, one usually has to bend the flexible printed circuit before fixing and attaching. However, due to the rigidity of the conventional flexible printed circuit, residual stress is generated at the bent part that may change the deflecting angle. Therefore, the alignment becomes hard to control during automatic assembly processes and not each flexible printed circuit can be nicely attached onto the inkjet cartridge. If one tries to increase the strength in deflection, it is quite possible to damage or break the conductive circuit on the flexible printed circuit. Moreover, in the above-mentioned conventional manufacturing process, the deflecting part of the soft circuit is not coated with any cover layer for protection, it is likely to be damaged when the cartridge is mounted or scratched. Another disadvantage of the conventional manufacturing technique is that the residual stress generated during the deflecting process may result in the crook problem.
To improve the deflecting process, to conquer the residual stress problem, and to protect the deflecting part, the invention proposes a better structure and manufacturing process.
An objective of the invention is to provide a manufacturing process for the flexible printed circuit of inkjet printheads so that the raw material is already pre-bent. It can effectively reduce the residual stress when further deflecting the flexible printed circuit, enhance the smooth attachment to the cartridge, and protect the conductive circuit at the deflecting part from scratches.
The steps of the disclosed manufacturing process include: (1) prepare a flexible printed circuit substrate includes a window therethrough at a predetermined deflecting part; (2) coat a metal layer on the substrate as a conductive metal layer; (3) etch the metal layer using a photolithography procedure to form a conductive circuit on the flexible printed circuit; and (4) apply a cover layer (solder mask such as epoxy or acrylic resins) at the window. A flexible printed circuit thus produced is pre-bent, easy to attach and align, and has less residual stress and a cover layer or film at the bent part.